Save partial model objects and junk

create_form_partials.rb

class CreateFormPartial < ActiveRecord::Migration
  def self.up
    create_table :form_partials do |t|
      t.string      :persistence_hash, :null => false
      t.binary      :data, :null => false
      t.boolean     :saved, :default => false
      t.references  :user, :null => false

      t.timestamps
    end

    add_index :form_partials, [:persistence_hash, :user_id]
  end

  def self.down
    drop_table :form_partials
  end
end

form_partial.rb

##
# Used to store models and presenters in between multipage form pages.
# Can also store and retrieve any other object you want.
#
# @author Josh Lindsey
#
class FormPartial < ActiveRecord::Base
  belongs_to :user

  validates_presence_of :persistence_hash, :data, :user
  validates_uniqueness_of :persistence_hash

  class << self
    ##
    # Store an object, bound to a single user for security.
    #
    # @param [Object] object The object to Marshal and store
    # @param [User] user The user object (usually passed in with current_user)
    # @param [Boolean] saved Set to true to override {clean_old_partials} date checking on this record
    #
    # @return [String] The persistence hash generated for this record, to {retrieve} it later
    #
    # @raises [InvalidRecord] On validation failure
    #
    # @author Josh Lindsey
    #
    def store(object, user, saved = false)
      params = {}
      params[:data] = Marshal.dump object
      params[:persistence_hash] = generate_hash
      params[:saved] = saved
      params[:user] = user
   
      model = self.create! params 

      params[:persistence_hash]
    end

    ##
    # Update an already stored object, given the hash and user it belongs to.
    #
    # @param [Object] object The updated object
    # @param [User] user The user object
    # @param [String] hash The persistence hash for the object
    # @param [Boolean] saved Override {clean_old_partials} date checking
    #
    # @return [Boolean] True on success, false on failure
    #
    # @author Josh Lindsey
    #
    def update(object, user, hash, saved = nil)
      params = {}
      params[:data] = Marshal.dump object
      params[:saved] = saved unless saved.nil?

      model = self.find_by_persistence_hash_and_user_id(hash, user.id)
      model.update_attributes params
    end

    ##
    # Shortcut method to {store} an object with saved set to true.
    #
    # @param [Object] object The object to save
    # @param [User] The user object
    # 
    # @return [String] The persistence hash generated by {store}
    #
    # @see {store} for actual logic
    #
    # @author Josh Lindsey
    #
    def save(object, user)
      store(object, user, true)
    end

    ##
    # Retrieve a stored object given the user and hash it's associated with.
    #
    # @param [User] The user object
    # @param [String] The persistence hash
    #
    # @return [Object] Whatever object was stored. *Note*: If that object was an ActiveRecord
    #   model, you will have to reestablish the database connection before calling save on it.
    #
    # @author Josh Lindsey
    #
    def retrieve(user, hash)
      str = self.find_by_persistence_hash_and_user_id(hash, user.id).data
      return if str.nil?
      Marshal.load str
    end

    ##
    # Cleans out old partials (seriously). Should be run as a cron with script/runner or the like.
    #
    # @param [Date] date All records last updated before this date, and with saved == false are destroyed
    #
    # @author Josh Lindsey
    # 
    def clean_old_partials(date = 1.day.ago)
      partials = self.find(:all, :conditions => ['updated_at <= ? AND saved = 0', date])
      partials.each { |partial| partial.destroy }
    end

    ##
    # Generate a random SHA1 hash for storing new records.
    #
    # @return [String] The hash generated
    #
    # @author Josh Lindsey
    #
    def generate_hash
      Digest::SHA1.hexdigest rand.to_s
    end
  end
end

form_partial_test.rb

require 'test_helper'

class FormPartialTest < ActiveSupport::TestCase
  should_validate_presence_of :persistence_hash, :data, :user

  context "The FormPartial model" do
    setup do
      @stored_object = Child.make
      @user = User.make
      @token = FormPartial.store @stored_object, @user
    end

    should "store and retrieve objects" do
      obj = FormPartial.retrieve(@user, @token)
      assert_instance_of Child, obj
      assert_equal @stored_object, obj
    end

    should "update existing objects" do
     obj = FormPartial.retrieve(@user, @token)
     obj.first_name = "Tom"
     
     assert FormPartial.update(obj, @user, @token)

     updated = FormPartial.retrieve(@user, @token)
     assert_equal obj, updated
    end

    should "clean out its table" do
      FormPartial.record_timestamps = false

      assert_equal 1, FormPartial.count

      FormPartial.store @stored_object, @user
      FormPartial.last.update_attribute :updated_at, 5.days.ago
      assert_equal 2, FormPartial.count

      FormPartial.store @stored_object, @user
      FormPartial.last.update_attributes :updated_at => 5.days.ago,
                                         :saved => true
      assert_equal 3, FormPartial.count

      FormPartial.clean_old_partials

      assert_equal 2, FormPartial.count
    end
  end
end

This was made for an internal project, so obviously change the Child and User objects in the test to whatever you want to test it on.

The test is using Test::Unit, shoulda, and machinist (with my fork of random_data).

The documentation comments are in YARDOC syntax.